Systems and Processes for Improving Distillate Yield and Quality

ABSTRACT

Systems and processes for improving quality and yield of one or more distillate products generated in a distillation column are disclosed. The system comprises a feed inlet distributor that reduces the amount of liquid entrained in vapor rising from the feed zone of the distillation column, a wash zone collection apparatus having an improved design for collecting slop wax falling from a liquid/vapor contacting structure provided in the wash zone, a recirculation subsystem for recirculating at least a portion of the collected slop wax to the top of the wash zone for distribution as wash oil, and a control subsystem. The feed inlet distributor ensures a horizontal fluid flow path free of transverse surfaces thereby minimizing atomization of liquid droplets entrained in vapor in the feed stream.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit, and is a continuation applicationof prior U.S. application Ser. No. 13/050,521 filed Mar. 17, 2011entitled “Systems and Processes for Improving Distillate Yield andQuality,” which claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application Ser. No. 61/340,576 filed on Mar. 19,2010, which is incorporated herein by reference in its entirety.

BACKGROUND

Various technologies and techniques exist for separating mixtures ofliquids into their individual components. Distillation—specificallyfractional distillation—is the most common form of separation technologyused in the chemical process industries and is a critical part ofpetroleum refining, petrochemical and chemical production, and naturalgas processing. Oil refineries, for example, employ fractionaldistillation to separate crude oil into useful components comprised ofdifferent hydrocarbons with different boiling points.

SUMMARY

Systems and processes for improving the yield and quality of distillateobtained from fractionation of black oil streams are disclosed.Embodiments of the invention relate to structural and designimprovements to distillation columns as well as distillation processimprovements that generate significant advantages over conventionalsystems and processes.

Throughout this entire disclosure, including the detailed descriptionand the claims, “a portion of” a substance may refer to an entire amountof the substance or any lesser amount thereof.

According to an embodiment of the invention, a system for improvingyield and quality of one or more distillate products generated in adistillation column is disclosed. The distillation column comprises afeed zone, a wash zone located above the feed zone, and a fractionationzone located above the wash zone. The wash zone has disposed therein aliquid/vapor contacting structure a wash oil distributor fordistributing wash oil to the contacting structure.

The system according to the above-described embodiment of the inventioncomprises a feed inlet distributor that reduces an amount of liquidentrained in a vapor rising from the feed zone, a wash zone collectionapparatus having an improved design for collecting slop wax falling fromthe wash zone, a recirculation subsystem for recirculating a portion ofthe slop wax withdrawn from the wash zone collection apparatus, and acontrol subsystem for controlling other subsystems.

The recirculation subsystem comprises a pump, a first conduit forconducting collected slop wax from the wash zone collection apparatus tothe pump, a second conduit for recirculating a portion of the pumpedslop wax to the wash oil distributor for distribution as wash oil to thecontacting structure, and a third conduit for conducting a portion ofthe pumped slop wax to equipment located externally to the distillationcolumn.

The control subsystem may comprise means for controlling a flow rate ofthe recirculated portion of the pumped slop wax and means forcontrolling a flow rate of the portion of the pumped slop wax conductedto the external equipment.

In accordance with one or more embodiments of the invention, therecirculation subsystem may further comprise a means for combining aportion of a distillate product collected by a distillate productcollector disposed in the fractionation zone with the recirculatedportion of the slop wax to form a combined stream that is conducted tothe wash oil distributor for distribution as wash oil to the contactingstructure. The slop wax recirculation rate in embodiments of theinvention is several times higher than the wash oil rate in conventionalapparatuses, and as such, the rate at which distillate product, if any,is conducted to the distributor is a small fraction of the rate requiredin conventional apparatuses to remove liquid entrained in vapor passingthrough the wash zone.

In certain embodiments of the invention, the system may further comprisean insulating apparatus comprising one or more insulating materialsapplied to the distillate product collector to reduce condensation ofvapor on a bottom surface thereof.

According to one or more embodiments of the invention, the wash zonecollection apparatus comprises one or more transverse collector troughsinclined towards an opening that provides for fluid communication withthe recirculation subsystem and a plurality of lateral troughs disposedin two or more layers and inclined towards the one or more transversecollector troughs, wherein the lateral troughs of each layer arestaggered with respect to the lateral troughs of an adjacent layer.

According to one or more embodiments of the invention in which thedistillation column includes a tangential feed entry nozzle, atangential feed inlet distributor is provided that comprises ahorizontally disposed annular ring extending around an entirecircumference of the circumferential wall of the distillation column,and a cylindrical skirt connected to an inner edge of the annular ringand extending downward therefrom. The annular ring, the cylindricalskirt, and the circumferential wall of the distillation column togetherdefine an open-bottomed tunnel within the distillation column into whichthe fluid feed stream is injected or channeled via the tangential feedinlet. The tunnel is free of any surface transverse to the substantiallytangential flow path of the fluid feed stream thereby reducingatomization of entrained liquid in the fluid feed stream.

In alternative embodiments of the invention in which the feed entrynozzle is radial to the distillation column, a radial feed inletdistributor is provided that comprises a roof plate that extendssubstantially across an entire diameter of the distillation column and askirt comprising opposing walls laterally spaced from each other about adistance equal to a diameter of the feed inlet and extending downwardsfrom the roof plate about a distance equal to the diameter of the feedinlet. The opposing walls of the skirt may terminate prior to reaching adistal end of the circumferential wall of the distillation column. Theroof plate and the opposing walls of the skirt together define anopen-bottomed tunnel within the distillation column into which the fluidfeed stream is injected or channeled via the radial feed inlet.

The radial feed inlet distributor further comprises a feed splitterprovided in proximity to where the opposing walls of the skirtterminate, the feed splitter splitting the fluid feed stream bilaterallyinto two smaller fluid feed streams directed in opposing horizontaldirections and along flow paths substantially tangential to thecircumferential wall of the distillation column. The tunnel is free ofany surface transverse to the initial radial flow path of the fluid feedstream or the horizontal tangential flow paths of the smaller fluid feedstreams thereby reducing atomization of entrained liquid in the fluidfeed stream.

According to an embodiment of the invention, a process for improvingquality and yield of one or more distillate products generated in adistillation column is disclosed. The process comprises: providing atangential or radial feed inlet distributor within the distillationcolumn in dependence on whether the feed inlet is tangential or radialto the column, collecting slop wax falling from the contacting structureusing a wash zone collection apparatus disposed in the wash zone, andrecirculating a portion of the slop wax to the wash oil distributor fordistribution as the wash oil to the contacting structure. In a morespecific embodiment, the process further comprises conducting collectedslop wax from the wash zone collection apparatus to a pump,recirculating a portion of the pumped slop wax to the wash oildistributor, and conducting a portion of the pumped slop wax toequipment located externally to the distillation column.

The process may further comprise combining a portion of distillateproduct collected by a distillate product collector disposed in thefractionation zone with the recirculated portion of the slop wax to forma combined stream, conducting the combined stream to the wash oildistributor, and distributing the combined stream as the wash oil to thecontacting structure. In certain embodiments, the process mayadditionally comprise applying one or more insulating materials to thedistillate product collector to reduce condensation of vapor on a bottomsurface thereof.

These and other embodiments of the invention are described in furtherdetail through reference to the following drawings in the detaileddescription that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a conventional distillationsystem.

FIG. 2 is a schematic representation of a system in accordance with oneor more embodiments of the invention.

FIGS. 3A-3C depict various plan and/or sectional views of a wash zonecollection apparatus in accordance with one or more embodiments of theinvention.

FIGS. 4A and 4B depict plan and sectional views, respectively, of atangential feed inlet distributor in accordance with one or moreembodiments of the invention.

FIGS. 5A and 5B depict plan and elevation views, respectively, of aradial feed inlet distributor in accordance with one or more alternateembodiments of the invention.

FIG. 6 is a photograph of two samples of HVGO product obtained by theexperimental testing.

DETAILED DESCRIPTION

Systems and processes disclosed herein are applicable to a wide range ofpetroleum refining processes (e.g. atmospheric distillation of crudeoil, vacuum distillation of reduced crude, fractionation of effluentfrom pyrolysis furnaces), and may be employed, for example, in the maincolumns of Delayed Coking, Fluid Catalytic Cracking and ResidueHydrotreating Units. Moreover, systems and processes according toembodiments of the invention may also be used in connection withnumerous other industry recovery processes such as, for example, tarsands bitumen and coke oven distillate recovery.

Although the invention will be described primarily through reference toembodiments involving the processing of reduced crude, it should benoted that the invention is not limited to such embodiments, and, asnoted above, systems and processes of the invention are applicable toany distillation process in which the column feed is at least partiallyvaporized and comprises non-volatile components which, if allowed tocontaminate the distillate, are deleterious to its subsequentprocessing. More specifically, embodiments of the invention areapplicable to distillation columns that process feed streams thatinclude components that are not volatile under process conditions (e.g.asphaltenes and organometallic compounds), but which, if allowed tocontaminate the distillate by entrainment of liquid droplets in thevapor rising from the feed inlet point, discolor the distillate andproduce significant adverse effects on the activity and selectivity ofcatalysts used in connection with further processing of the distillate.

One of the first process units that crude oil enters for processing isthe Atmospheric Crude Fractionating Column (hereinafter “Crude Unit”).The reduced crude obtained from this process is typically furtherdistilled in a fractionating column operating under sub-atmosphericpressure (a Vacuum Crude Fractionating Unit or more commonly known as a“Vacuum Unit”) to separate additional distillate from the heavierfraction that contains essentially all metals and asphaltenes present inthe crude oil. The vacuum distillate recovered from the Vacuum CrudeFractionating Unit is generally converted to more valuable products bydownstream processes such as Fluid Catalytic Cracking, Hydrotreating,and Hydrocracking. Those processes employ catalysts whose activity andselectivity are reduced by the presence of metals and asphaltenes in thevacuum distillate. Accordingly, a strong economic incentive exists forminimizing the entrainment of liquid containing those contaminants inthe distillate product.

Although embodiments of the invention are discussed primarily inconnection with the processing of a feed stream fed to a Vacuum Unit inwhich the operating pressure is low, the feed inlet velocities and vaporupflow are high, and the liquid entrainment in the vapor stream isespecially severe, the operating principles and advantages ofembodiments of the invention are applicable to any distillation systemand process in which it is desirable to prevent liquid entrainment inthe vapor phase rising from the feed point.

FIG. 1 depicts a sectional view of a portion of a conventional VacuumUnit distillation column and accompanying elements disposed externallyto the column. The column 100 includes a packed Heavy Vacuum Gas Oil(HVGO) section 101 where HVGO product, typically boiling between 650° F.and 1050° F., is condensed from the vapor rising through the column.Located below the HVGO section 101 is a draw tray 102 for collecting thecondensed HVGO product. An HVGO pump 110 recirculates at least a portionof the collected HVGO product back to the HVGO section 101 throughconduit 110 a. Flow controller 108 is provided for controlling a flowrate of the recirculated HVGO product through conduit 110 a via valve107. Pump 110 also pumps at least a portion of the collected HVGOproduct through conduit 110 b for further processing, for example, in aFCC Unit or a Hydrocracking Unit. Level controller 109 is provided forcontrolling a flow rate of distillate through conduit 110 b via valve111. Further, in conventional distillation apparatuses such as thatshown in FIG. 1, the HVGO pump 110 additionally pumps a significantportion of the collected HVGO product through conduit 110 c for use aswash oil in wash zone 100 b.

The portion of the distillation column 100 depicted in FIG. 1 can besegmented into three zones. A fractionation zone 100 a encompasses theHVGO section 101 and the draw tray 102. The wash zone 100 b encompassesa region of the column extending between the bottom of draw tray 102 andthe bottom of a collection tray 105. The feed zone (or flash zone) 100 cencompasses a region of the column between the bottom of collection tray105 and a position in relative proximity to the feed inlet 106 to thecolumn.

A fluid feed stream 106 a generally enters the vacuum column 100 from afired heater and comprises mostly vapor by weight and almost all vaporby volume. As a result of the high feed stream velocities in the feedconduit from the heater to the column, a mist flow is generated withliquid entrained as small diameter droplets within the vapor. In thefeed zone 100 c, a portion of the liquid phase in the feed stream 106 afalls out of the rising vapor of the stream by gravimetric separationalone. In the wash zone 100 b, entrained liquid droplets are removedfrom the rising vapor of the feed stream 106 a by scrubbing the vaporwith a liquid (i.e. wash oil) while using trays or packing to enhanceliquid/vapor contact.

In conventional apparatuses, a portion of the heaviest distillateproduct—obtained by condensation in the fractionation zone located justabove the wash zone—serves as the sole source of the wash oil used toremove entrained liquid droplets from the vapor rising through the washzone. For example, in a conventional vacuum column such as that depictedin FIG. 1, a significant portion of the heaviest distillate product(i.e. the condensed HVGO product collected by draw tray 102) is pumpedby HVGO pump 110 to the wash zone 100 b via conduit 110 c for use aswash oil. Valve 113 controls the flow rate of the wash oil in responseto a signal communicated by flow controller 112. The wash oil issupplied to one or more liquid distributors 103 provided at a topportion of packing 104 in the wash zone 100 b. As vapor in the fluidfeed stream 106 a rises upwards in the column 100 through the packing104, the vapor is scrubbed with the wash oil leading to removal of aportion of the liquid entrained in the vapor.

A collection tray 105 is provided at the bottom of the wash zone 100 bto collect liquid falling from the packing 104. This liquid, also knownin the art as slop wax, is then conducted through conduit 117 to pump115. A level controller 114 is provided to determine an amount of slopwax that has accumulated in the collection tray 105 and communicate asignal to valve 116 which controls the flow of slop wax through to fluidline 118. The slop wax is carried through fluid line 118 to furtherblending or recycling treatment systems. However, certain conventionaldistillation apparatuses do not include a slop wax collection tray orthe associated pump and instead allow the slop wax to fall past the feedzone to combine with the bottoms product from the column.

There are several drawbacks to conventional distillation apparatusesthat utilize a significant portion of the heaviest distillate product aswash oil for removing liquid droplets entrained in vapor rising throughthe wash zone. First, the use of distillate product as wash oil clearlydecreases the yield of distillate, which is substantially more valuablethan the bottoms product. The significant economic costs associated withthe use of distillate as wash oil creates a strong incentive to minimizethe amount of the distillate used. This is typically accomplished byminimizing the rate at which distillate is provided as wash oil to thewash zone.

However, minimization of the wash oil rate is subject to the constraintthat the rate must be high enough to provide wetting of the packingsufficient to limit coke formation to an economically acceptable rate.In order to prevent the development of unwetted areas in the packing 104where coke can accumulate, the flow rate of wash oil distributed to thetop of the wash zone 100 b in conventional apparatuses must besufficient to maintain the packing 104 in a thoroughly wetted condition,particularly, a bottom portion of the packing which is especially proneto coke accumulation. The need to maintain a sufficiently high wash oilflow rate so as to both capture entrained liquid and reduce/minimizecoking runs counter to the strong financial incentive to minimize thewash oil rate to obtain greater distillate yields.

Experimental and operational data has shown that lower liquid flow ratesover the wash zone packing as well as poorer liquid distribution acrossthe packing leads to an increase in coke deposition and accumulationrates. Moreover, the accumulation of coke deposits on the packingreduces the efficiency of entrained liquid removal from the vapor risingthrough the packing. In fact, there exists a threshold level of cokeaccumulation at which the efficiency of entrained liquid removal isreduced to such an extent that the distillation unit must be shut downand the packing disassembled and cleaned of the coke. The resultantdowntime caused by this coke removal maintenance operation comes at anenormous economic cost to the refinery, particularly when the processunit that is being shut down affects the operation of valuabledownstream units.

To balance the competing objectives of capturing entrained liquid fromthe vapor rising through the column, minimizing loss of distillateyield, and maintaining wash zone packing in a sufficiently wettedcondition so as to prevent excess accumulation and deposition of coke,those of ordinary skill in the art have chosen to direct their effortsat modifying the mechanical design of the packing and the mechanism bywhich wash oil is distributed onto the packing. Efforts have also beenfocused on modifying the geometry of internal structures within the feedzone with the avowed aim of achieving a uniform velocity of the risingvapor across the cross section of the column prior to reaching the washzone.

To assist in these efforts, those skilled in the art have employedsophisticated Computational Fluid Dynamics (“CFD”) programs to designfeed inlet devices that attempt to uniformly distribute the vaporflowing up through the column. In addition, efforts have also focused ondesigning beds of structured packing and distributors that attempt tominimize the amount of liquid wash necessary to remove entrained liquidfrom the vapor while still preventing excess accumulation of coke. Theseefforts, however, have resulted in an only marginal reduction in theamount of distillate that must be supplied to the wash zone as wash oilin order to maintain the sufficiently high liquid flow rates required toremove entrained droplets from the vapor and to prevent excessaccumulation of coke in the wash zone packing.

Systems and processes according to embodiments of the inventioneliminate the tension present in the operation of conventionalapparatuses between preventing excess coke accumulation in the packingand minimizing loss of distillate yield. Embodiments of the inventionare directed to novel systems and processes that contradict conventionalwisdom in the art and essentially eliminate both the loss of distillateyield and the excess accumulation of coke in the wash zone packing thatoccurs in conventional systems while achieving essentially completeremoval of entrained liquid from the vapor rising through the wash zone.

According to one or more embodiments of the invention, a system forimproving quality and yield of one or more distillate products generatedin a distillation column is disclosed. The distillation column comprisesa feed zone, a wash zone located above the feed zone, and afractionation zone located above the wash zone.

The wash zone has disposed therein a liquid/vapor contacting structureand a wash oil distributor that distributes a liquid stream onto theliquid/vapor contracting structure without producing fine droplets thatcan become entrained in the vapor rising through the distillatecollector into the fractionation zone. The contacting structure maycomprise trays or packing that enhance liquid/vapor contact to reduce anamount of liquid entrained in vapor rising through the wash zone. Thesystem further comprises a feed inlet distributor that reduces an amountof liquid entrained in a vapor stream rising through the wash zone, awash zone collection apparatus having an improved design for collectingslop wax falling from the contacting structure, a recirculationsubsystem, and a control subsystem. The recirculation and controlsubsystems will be described in more detail through reference to FIG. 2,the wash zone collection apparatus through reference to FIGS. 3A-3C, andthe feed inlet distributor through reference to FIGS. 4A-5B.

A key feature of the recirculation subsystem is the recirculation orrecycling of at least a portion of the slop wax collected by the washzone collection apparatus back to the top of the wash zone for use aswash oil. Because of its high metals and asphaltene content, thoseskilled in the art have not previously considered the benefits ofrecycling collected slop wax to the top of the wash zone for use as washoil. In fact, conventional wisdom has repeatedly taught away fromrecycling the black, viscous slop wax to the top of the wash zone foruse as wash oil based on the belief that use of the slop wax wouldresult in poor liquid distribution throughout the packing and thedevelopment of dry sections vulnerable to coke accumulation. Inconventional systems, this collected liquid is either combined with thebottoms product or recycled to the charge heater.

Applicants recognized—contrary to the pervasive teachings of the priorart—that slop wax recirculation in accordance with embodiments of theinvention in fact minimizes coke accumulation by allowing for high washoil rates that are not economically feasible when distillate alone isused as the wash oil. By virtue of the recirculation of slop wax to thetop of the wash zone for use as wash oil in accordance with embodimentsof the invention, distillate is no longer used as a primary source forthe wash oil, if at all, and significantly higher distillate yields areobtained. Moreover, as will be described in greater detail hereinafter,minimizing the wash oil flow rate is no longer a consideration inembodiments of the invention, and as a result, greater entrained liquidremoval rates and lower coke accumulation rates are observed as comparedto conventional apparatuses.

FIG. 2 depicts a sectional view of a portion of a distillation column200 and elements external thereto in accordance with one or moreembodiments of the invention. Any elements shown in FIG. 2 that are notseparately described through reference to FIG. 2 perform functionssimilar to corresponding elements described through reference to FIG. 1.The distillation column comprises a fractionation zone 200 a, a washzone 200 b located below the fractionation zone 200 a, and a feed zone200 c located below the wash zone 200 b. The wash zone has disposedtherein a liquid/vapor contacting structure 204 and a wash oildistributor 203 for distributing wash oil to the contacting structure204.

Still referring to FIG. 2, the system according to embodiments of theinvention includes a feed inlet distributor (not shown), a wash zonecollection apparatus 205 disposed in the wash zone 200 b for collectingslop wax falling from the contacting structure 204, a recirculationsubsystem, and a control subsystem.

The recirculation subsystem comprises conduit 217 for conductingcollected slop wax from the wash zone collection apparatus 205 to pump215. The recirculation subsystem further comprises conduit 218 forrecirculating a portion of the slop wax pumped from pump 215 to the washoil distributor 203 for distribution as wash oil to contacting structure204, and conduit 219 for conducting a portion of the pumped slop wax(i.e. that portion not recirculated to the top of the wash zone) toexternal equipment for further treatment (e.g. the inlet of a chargeheater) or for commingling with the heavy liquid bottoms product.

The portion of the slop wax recirculated through conduit 218 and theportion of the slop wax conducted through conduit 219 togetherconstitute a total amount of slop wax pumped from the wash zonecollection apparatus 205. In one or more embodiments of the invention,the portion of the slop wax recirculated through conduit 218 representsa majority of the slop wax pumped from the wash zone collectionapparatus 205. Corrosion inhibitors and/or antifoulants may in certainembodiments be added to the recirculated portion of the slop wax or toother system streams.

The control subsystem according to embodiments of the invention maycomprise a level controller 214 that determines an amount of slop waxthat has accumulated in the wash zone collection apparatus 205 andcommunicates a signal to valve 216 to control the flow of that portionof the slop wax conducted through conduit 219 to further blending orrecycling treatment systems. The control subsystem may further compriseflow controller 220 that communicates a signal to valve 221 forcontrolling a flow of the recirculated portion of the slop wax throughconduit 218. In alternate embodiments of the invention, the flow of thatportion of the slop wax conducted through conduit 219 may be controlledby a flow controller.

It should be noted that the invention is not limited to the particulararrangement shown in FIG. 2 and that numerous other configurations andarrangements are within the scope of the invention. For example, inaccordance with one or more additional embodiments of the invention, thewash zone 200 b may comprise one or more wash zone sections and the slopwax that is recycled to the top of the wash zone 200 b for use as washoil may be obtained from anywhere in the wash zone 200 b below the washcolumn inlet through which wash oil is supplied to the wash zone 200 b.Each wash zone section may comprise a contacting structure, adistributor provided above the contacting structure for distributingwash oil to the contacting structure, a wash zone collection apparatusprovided below the contacting structure for collecting slop fax fallingfrom the contacting structure, and a means for recirculating a portionof the collected slop wax to the distributor in the same wash zonesection for distribution as wash oil.

In contrast to the streams of HVGO and Light Vacuum Gas Oil (LVGO)product that are typically recirculated back to the HVGO and LVGOsections of a vacuum column, respectively, the removal of heat from thatportion of the slop wax that is recirculated from the wash zonecollection apparatus 205 to the top of the wash zone 200 b is neithernecessary nor desired in embodiments of the invention. Because nothermal energy is removed from the recirculated slop wax, condensationof vapor flowing up through the wash zone 200 b from the feed zone 200 cdoes not occur.

The contacting structure 204 may comprise one or more types of packingmaterial including one or more trays, one or more beds of loose packing,and/or one or more layers of structured packing. As previously noted,the goal of packing designers has heretofore been to design packing thatminimizes the wash oil rate necessary to obtain desired entrained liquidremoval rates while maintaining the packing in a sufficiently wettedcondition, because increased use of wash oil in conventionaldistillation systems equates to an increase in the loss of valuable feedto downstream processes.

In contrast, according to embodiments of the invention, the contactingstructure 204 can be subjected to significantly higher liquid flow ratesbecause the wash oil comprises primarily, if not solely, recirculatedslop wax rather than expensive distillate, and is thus much lesssensitive to the performance of the wash oil distributor. Moreover, dueto the high liquid flow rate, the contacting structure 204 is moreresistant to the channeling of vapor that conventional designs are proneto and which has been known to produce dry areas vulnerable to cokeaccumulation. The contacting structure 204 according to embodiments ofthe invention is liberally flushed with liquid that captures—as it fallsthrough the contacting structure—liquid entrained in vapor risingthrough the wash zone. Thus, the contacting structure 204 remains cleanand functional for longer periods of time than in conventional systems.

The distributor in conventional systems is designed and sized so as tofunction with only a small flow rate of wash oil to the packing. Inembodiments of the invention, however, it is economically feasible tomaintain wash oil flow rates that are several times higher than inconventional systems, and thus the ability of the wash oil distributorto uniformly distribute wash oil to the contacting structure is not asignificant concern. As such, the distributor 203 according toembodiments of the invention need not be designed for maintaining auniform distribution of a low flow density of liquid, but instead may bedesigned for complete wash oil cross-sectional coverage of thecontacting structure 204 by a relatively high wash oil flow rate. Forexample, the wash oil distributor 205 may comprise robust spray nozzlesor even overflow troughs capable of high liquid flow rates. Applicantshave recognized that modern spray nozzles with large openings and moderntrough distributors may advantageously be employed as they are able tohandle liquids containing considerable suspended solids. Further,according to embodiments of the invention, the liquid flow densitythrough the contacting structure 204 is sufficient to carry out anysuspended solids. Moreover, the distributor 204 is specifically designedto distribute a liquid stream onto the liquid/vapor contractingstructure without producing fine droplets that can be entrained in thevapor rising through the distillate collector into the fractionationzone.

Applicants have determined that an amount of liquid that remainsentrained in the upward flowing vapor after scrubbing with wash oil isinversely related to the wash oil flow rate per unit of cross-sectionalarea of the packing. Experimental testing has confirmed that theincreased wash oil flow rates capable of being maintained in embodimentsof the invention are accompanied by only a negligible (if any) loss ofdistillate and result in considerably less entrained heavy materialappearing in the distillate product than in conventional systems.Because embodiments of the invention decouple the wash oil flow ratefrom the loss of valuable distillate, almost all of the materialcondensed in the HVGO section 201 can be recovered as HVGO productessentially free of asphaltenes and non-volatile organometalliccompounds. A prohibitively expensive amount of distillate yield wouldneed to be sacrificed in conventional systems in order to obtaintheoretically high enough wash oil flow rates to produce entrainedliquid removal rates comparable to those obtained in embodiments of theinvention.

In order to, for example, limit the concentration of entrained liquid inthe portion of the slop wax that is recirculated back to the top of thewash zone for use as wash oil, in certain embodiments of the invention,the recirculation subsystem may further comprise a means for combining aportion of a distillate product collected by distillate productcollector 202 with the portion of the slop wax recirculated throughconduit 218. More specifically, a portion of the distillate pumped frompump 210 may be diverted through conduit 210 c and combined with therecirculated portion of the slop wax via a juncture between conduit 218and conduit 210 c. Flow of the distillate product through conduit 210 cmay be controlled by flow controller 212 which communicates a signal tovalve 213. In alternate embodiments of the invention, flow of thedistillate through conduit 210 c may be controlled by level controller214. In those embodiments of the invention in which a portion of thecollected distillate is combined with the recirculated portion of theslop wax, the amount of distillate added is miniscule compared toconventional designs. For example, in one or more embodiments of theinvention, the amount of distillate added to the wash oil may constituteabout ten percent or less of the wash oil by weight.

During experimentation, Applicants unexpectedly observed that even whenthe addition rate of collected distillate to the wash oil was reduced tozero, slop wax continued to be pumped from the wash zone collectionapparatus 205 and the portion of the slop wax recirculated back to thetop of the wash zone 200 b for use as wash oil was more dilute thannecessary to ensure complete capture of the entrained liquid in thevapor rising through the wash zone 200 b.

Applicants reasoned that because there is no significant change intemperature across the wash zone 200 b in embodiments of the invention,the temperature at the top of the wash zone 200 b was higher than thetemperature of the distillate product collected in the distillateproduct collector 202. Applicants further reasoned that this temperaturedifferential was causing hot vapor rising past the wash zone 200 b tocondense on the bottom of the relatively cool distillate productcollector 202 (e.g. HVGO draw tray) thereby diluting the recirculatedslop wax more than necessary to ensure capture of essentially all liquidentrained in the rising vapor. That is, the small amount of heattransfer across the distillate product collector 202 is more thansufficient to provide the small amount of liquid that may be necessaryto dilute the wash oil in order to remove all entrained material in thevapor rising through the wash zone.

Accordingly, based on these observations, the system according toembodiments of the invention may further comprise an insulationapparatus comprising one or more insulating materials applied to asurface of the distillate product collector 202. The one or moreinsulating materials may comprise a castable refractory applied to anupper surface of a floor of the distillate product collector 202 inorder to reduce condensation of vapor on a bottom surface of thereof.This reduction in vapor condensation may in turn require the addition ofa very small amount of collected distillate to the recirculated slop waxin order to keep the concentration of captured entrained liquid in thewash oil low enough for the wash oil to continue to be effective inremoving essentially all of the entrained liquid from the rising vapor.

Of particular advantage is that the addition of one or more insulatingmaterials to the distillate product tray coupled with the addition of asmall amount of the collected distillate to the wash oil may in certainembodiments produce a greater distillate product yield than if thedistillate product collector is not insulated and no collecteddistillate is added to the wash oil. That is, because the flow ofmake-up distillate necessary to sustain the performance of the wash zonegenerally, and the wash oil in particular, may be less than the amountof distillate condensed on a bottom surface of the distillate productcollector, the distillate yield may in fact be maximized by insulatingthe distillate product collector 202 immediately above the wash zone 200b. Reducing the amount of condensation on the underside of thedistillate product collector 202 reduces the uncontrolled loss ofpotential distillate to the recirculated wash oil and transfers controlof the dilution of the wash oil with collected distillate product toflow controller 212.

In one or more exemplary embodiments of the invention, an operatingratio of 19:1 recycled wash oil to fresh distillate results in effectiveremoval of entrained liquid from the rising vapor while providing easeof control. According to an exemplary process of the invention,initially fresh distillate alone is provided as wash oil to the washzone. Subsequently, the amount of distillate added to the wash oil isprogressively reduced while the rate at which collected slop wax isrecycled to the wash zone is concomitantly increased. The addition rateof distillate to the wash oil may be adjusted based on: (1) the rate ofdilution needed to keep the collected slop wax pumpable, and/or (2) theamount of fresh distillate required to maintain essentially completecapture of the entrained liquid from the rising vapor.

Applicants conducted an experiment that compared the distillate yieldsobtained by a conventional distillation system and a system inaccordance with an embodiment of the invention. The 95% distillationpoint for the conventional distillation system based on the industrystandard ASTM Method D-1160 distillation of HVGO product was 1050° F.However, after modifications were made to the conventional system toproduce a system in accordance with an embodiment of the invention, the95% distillation point of the HVGO product increased to 1250° F. and thedistillate obtained was almost completely free of contamination byentrained feed liquid.

It is known in the art that conventional vacuum distillation units areincapable of yielding an HVGO product with the 95% distillation pointhigher than 1050° F. without increasing the charge heater outlettemperature to such an extent that excessive coking of the charge heaterand cracking of the feed stream results. Applicants unexpectedlydetermined that the 200° F. increase in the 95% distillation pointobtained by the system of the invention resulted in an increase in theHVGO product yield by about 5% of the fluid feed stream to the column.If the distillate yield is supplied as feed to an FCC unit, for example,it is estimated that this increase in the distillate yield canpotentially increase refinery profit by US$110 per incremental barrel ofFCC feed. To provide context for this estimation, the spot market priceof West Texas Intermediate crude oil was approximately US$90/barrel atthe time the estimate was made.

FIG. 6 is a photograph showing two samples of HVGO product obtained bythe experimental testing described above. The sample on the left is oneobtained using a conventional apparatus and the sample on the right isone obtained in the same vacuum column using a system in accordance withan embodiment of the invention. As is evident, the sample on the rightis almost completely free of darkening by the black entrained feedliquid. In addition, the sample on the right has a much higher end point(about 1250° F.) than the sample on the left (1050° F.) corresponding toabout a 5% increase in distillate yield.

In addition to the recycling of slop wax for use as wash oil, anothernovel aspect of systems according to embodiments of the invention is thedesign and structure of the wash zone collection apparatus.

FIGS. 3A-3C depict various plan and/or sectional views of a wash zonecollection apparatus in accordance with one or more embodiments of theinvention. The wash zone collection apparatus so depicted minimizesturbulence and thus pressure drop in the rising vapor in three primaryways: by minimizing the deflection of vapor as it rises through thecollection apparatus, by occluding less than 50% of the cross-sectionalarea of the column at any layer of the apparatus, and by not introducingany drag-inducing sharp edges in the vapor path.

FIG. 3A shows a plan view of the wash zone collection apparatus. Theapparatus 300 includes one or more center channels or troughs 301. Oneor more layers of lateral troughs may be provided so as to be inclinedtowards the center trough(s) 301. A single layer comprising lateraltroughs 303A is shown in the plan view of FIG. 3A.

FIG. 3B depicts a sectional view of the wash zone collection apparatustaken along Section 3B-3B in FIG. 3A. Two layers 302, 303 of lateraltroughs are provided. Layer 302 comprises lateral troughs 302A and layer303 comprises lateral troughs 303A. The lateral troughs 302A of layer302 are positioned so as to be staggered laterally with respect to thelateral troughs 303A of layer 303. The plurality of lateral troughs ineach layer may be substantially equal in width and each lateral troughin each layer may be spaced laterally from an adjacent trough in thesame layer by a distance of about 1.0 to about 1.2 times the width ofeach lateral trough. Moreover, each layer of lateral troughs may bespaced vertically from an adjacent layer by a distance about equal to adistance between adjacent lateral troughs in the same layer.

The staggering of the lateral troughs of one layer with respect to thelateral troughs of another layer such that each lateral trough in eachlayer is spaced laterally from an adjacent trough in the same layer by adistance of about 1.0 to about 1.2 times the width of each lateraltrough produces significant advantages over conventional slop waxcollectors. In particular, the design described above causes vaporflowing upward through the gaps between adjacent lateral troughs in alower layer to split on the bottom surface of a lateral trough in animmediately adjacent upper layer. This in turn directs liquid that haspassed through the contacting structure toward a center line of the gapbetween adjacent troughs in an upper layer and thus onto the center axisof a lateral trough in the lower layer. Accordingly, more effective slopwax collection is achieved.

To further minimize pressure drop across the wash zone collectionapparatus, the center channel or trough 301 as well as the lateraltroughs 302A, 303A may comprise rounded or V-shaped bottoms. In anexemplary embodiment of the invention, at least the upper edges of eachlateral trough may be curved with a radius of about 1 cm to about 2 cmabout 60 degrees toward the center axis of the lateral trough. Thisdesign not only provides adequate stiffness but also produces theunexpected additional advantage of reducing pressure drop across theapparatus and reducing re-entrainment of liquid droplets deposited onthe lower surfaces of the lateral troughs and forced upwards by therising vapor. The rounding of the upper edges of the lateral troughsinward out of the vapor path induces the rising vapor to direct dropletsfalling out of the wash zone packing toward the center axis of thetrough, which in turn allows a cross-sectional area occluded by eachlayer of lateral troughs to be less than about 50% of a cross-sectionalarea of the distillation column and the total plan area of the troughsto be less than 100% of the cross-sectional area of the column.Additionally, liquid residence time in the collection apparatus 300 isminimized by the narrowed V-bottomed surfaces and strong incline of thelateral troughs toward the central trough 301 as well as the incline ofthe central trough 301 toward an opening that provides for fluidcommunication with the recirculation subsystem. The rounded V-shape ofthe bottom surfaces of the lateral troughs also serves to minimize vapordrag.

As previously mentioned, a system according to one or more embodimentsof the invention additionally comprises a feed inlet distributor thatreduces or minimizes an amount of liquid entrained in a fluid feedstream fed to the distillation column. The gas velocity that will causeentrainment of a liquid droplet is proportional to the square of thedroplet's diameter. The amount of liquid entrained in the vapor risingthrough the wash zone is dependent on the velocity of the vapor, whichis a function of the vapor mass flow rate and specific volume, and thedistribution of droplet sizes in the feed liquid. In general, the morefinely atomized the feed liquid, the greater the level of entrainment.

FIGS. 4A and 4B depict plan and sectional views, respectively, of atangential feed inlet distributor 400 in accordance with one or moreembodiments of the invention. The tangential feed inlet distributor 400shown in FIGS. 4A and 4B distributes a fluid feed stream that enters thecolumn through a tangential feed inlet 401 along a flow pathsubstantially tangential to a circumferential wall 402 of the column.The feed distributor 400 comprises a horizontally disposed annular ring403 extending around an entire circumference of the circumferential wall402 of the distillation column, and a cylindrical skirt 404 connected toan inner edge of the annular ring 403 and extending downward therefrom.In certain embodiments of the invention, the annular ring 403 may extendfrom the circumferential wall 402 of the distillation column by adistance about equal to a diameter of the feed inlet 401 and thecylindrical skirt 404 may extend downward a distance equal to about 1.25times the diameter of the feed inlet 401.

The horizontal annular ring 403, the cylindrical skirt 404, and thecircumferential wall 402 of the distillation column together define anopen-bottomed tunnel within the distillation column into which the fluidfeed stream is injected or channeled via feed inlet 401. The tunneltemporarily segregates the incoming fluid from the vapor rising past thetunnel to allow the fluid to decelerate and the entrained liquid toseparate. The tangential flow path of the fluid feed stream exploitscentrifugal force and gravity to enhance gravimetric separation ofliquid from the vapor.

FIGS. 5A and 5B depict various views of a radial feed inlet distributor500 in accordance with one or more alternate embodiments of theinvention. In this embodiment, the feed inlet nozzle 501 is radial tothe vessel rather than tangential. The radial feed inlet distributor 500comprises a roof plate 504 that extends substantially across an entirediameter of the distillation column and a skirt comprising opposingwalls 503A, 503B laterally spaced from each other about a distance equalto a diameter of the feed inlet 501 and extending downwards from theroof plate 504 about a distance equal to the diameter of the feed inlet501. The opposing walls 503A, 503B of the skirt terminate prior toreaching a distal end of the circumferential wall 502 of thedistillation column. For example, the opposing walls 503A, 503B mayterminate a distance from the circumferential wall of the distillationcolumn equal to about one half of the diameter of the feed inlet 501. Afeed splitter or deflector 505 is provided in proximity to where theopposing walls 503A, 503B of the skirt terminate, the feed splitter 505splitting the fluid feed stream bilaterally into two smaller fluid feedstreams directed in opposing horizontal directions and along flow pathssubstantially tangential to the circumferential wall 502 of thedistillation column.

The fluid feed stream is injected or channeled via radial feed inlet 501into an open-bottomed tunnel defined by the roof plate 504 and theopposing walls 503A, 503B of the skirt. As such, the high velocityliquid in the vapor stream is constrained from spraying upward orlaterally and a bulk portion of the liquid falls out of the vapor streamthrough gravimetric separation. The feed splitter 505 converts theradial flow path of the fluid feed stream into bilateral horizontaltangential fluid flow paths, thereby exploiting the vapor velocity toenhance liquid separation by centrifugal force.

In an embodiment of the invention, the feed splitter 505 may comprise asharp-edged vertical bar 505A connected at an upper end to the roofplate 504 and extending downward therefrom a distance about 1.5 times adiameter of the feed inlet nozzle 501. The feed splitter 505 may furthercomprise symmetrically disposed deflector plates 505B, each plate beingrolled to form a quarter of the circumference of a vertical cylinderhaving a height equal to that of the vertical bar 505A. One verticaledge of each deflector plate may be attached to the vertical bar 505Awhile the other vertical edge lies along the circumferential wall 502 ofthe column.

Conventional inlet distributors comprise various types of vanes anddeflectors in the fluid feed stream path that exacerbate atomization ofentrained liquid in the feed stream. Further, panels, plates or otherdevices provided in the path of the high-velocity vapor produce eddycurrents in the flowing fluid. For every eddy in the downward direction,the velocity of the vapor elsewhere in the same horizontal plane mustincrease, thereby increasing the amount of entrained liquid. Moreover,structures disposed within the feed stream flow path convert thehorizontal velocity of the feed into a vertical velocity component thatcan exacerbate entrainment of liquid in the rising vapor.

Feed inlet distributors according to embodiments of the invention arefree of surfaces transverse to the feed fluid stream's tangential flowpath and thereby avoid the atomization of entrained liquid droplets andthe formation of eddy currents observed in conventional inletdistributors. The feed is allowed to travel tangentially along thecircumferential wall of the column unobstructed by any surface thatcould shatter liquid droplets or deflect the vapor vertically andexacerbate liquid entrainment in the rising vapor. Feed inletdistributors according to embodiments of the invention are thus able toexploit the horizontal velocity of the vapor stream to separate liquidgravimetrically as it flows tangentially along the wall of the column.

Additionally, in conventional systems, the increase in the amount ofentrained liquid in the vapor feed stream caused by impingement of thefeed stream against surfaces in the fluid flow path often necessitatesincreased washing action in the wash zone, which in turn requires anincrease in the amount of distillate that must be added to the wash oilcirculation to maintain its effectiveness. However, feed inletdistributors according to embodiments of the invention eliminate thisadditional disadvantage of conventional systems

Conventional wisdom in the art has heretofore advocated the installationof vanes of various shapes and orientations transverse to the fluid feedpath with the stated objective being to establish uniformity of verticalvelocity of the rising vapor below the wash oil collector. CFD modelinghas been used to design inlet distributors and associated impingementsurfaces that attempt to achieve a uniformity of distribution of therising vapor. A significant drawback of such modeling is that it hasfocused only on the vapor phase of the fluid feed stream without regardto the liquid phase.

Applicants have determined that uniformity of the vapor flow prior toreaching the wash zone is irrelevant to wash zone performance forseveral reasons. First, the velocity profile of the vapor as it risesthrough the wash zone is determined more by the design of the wash oilcollector than by the vapor velocity pattern below the collector.Second, with the high wash oil flow rate achieved by embodiments of theinvention, minor variations in the velocity of vapor entering the washzone packing are made more uniform by flow through the packing alone.Third, given the high liquid flow rates in the wash zone, the risingvapor is effectively washed despite any variations in vapor velocitybelow the packing.

Even assuming arguendo that feed inlet distribution subsystems accordingto embodiments of the invention are not capable of achieving as uniforma distribution of vapor velocities across the cross section of thecolumn above the feed zone as is achieved in conventional designs,embodiments of the invention are still capable of providing essentiallycomplete removal of entrained liquid. Applicants have determined thatthe uniformity of vapor distribution below the wash zone isinconsequential to removal of entrained liquid in the wash zone becausethe path of vapor flow through the wash oil collector has a far greaterinfluence on the distribution of vapor into the wash zone packing thanthe velocity profile below the collector. Moreover, any potentialadverse effect of non-uniform distribution of vapor leaving the feedzone is negated by the high wash oil flow rates capable of beingmaintained in embodiments of the invention, which ensure completewetting of the wash zone packing and essentially complete removal ofentrained material.

It should be noted that regardless of how well feed inlet distributorsaccording to embodiments of the invention are capable of performing,some entrainment of liquid in the vapor rising from the feed zone islikely to occur. The recirculation subsystem according to embodiments ofthe invention recirculates the majority of the slop wax that has fallenfrom the wash zone back to a top of the wash zone for use as wash oil.Only a miniscule portion of the distillate may be combined with therecirculated slop wax prior to distribution to the top of the wash zone.As such, because distillate addition to the wash oil is negligible,significantly higher wash oil flow rates can be maintained as comparedto conventional systems. Moreover, because the wash oil is at a highertemperature than the distilled liquid higher in the column, there isless condensation of the up-flowing vapor, and thus less loss ofdistillate yield. The end result is that the distillate product soobtained (e.g. HVGO product) contains negligible contamination byentrained material and is actually increased in yield. As an additionalbenefit, the modifications that must be made to conventional systems toarrive at embodiments of the invention do not require significantexpense.

While the invention has been described with respect to a particularnumber of embodiments, those having ordinary skill in the art willunderstand that numerous other embodiments involving variations ormodifications to the systems and processes described are also within thescope of the invention.

1. A process for improving quality and yield of one or more distillateproducts drawn from a distillation column whose feed stream is a mixtureof vapor and a liquid containing one or more components that aresubstantially non-volatile at column conditions, the distillation columncomprising a feed zone, a wash zone located above the feed zone havingdisposed therein a liquid/vapor contacting structure and a wash oildistributor for distributing wash oil to the upper surface of thecontacting structure, and means above the wash zone to remove the vaporproduct or liquid condensed therefrom, the process comprising:collecting a liquid (“slop wax”) falling from the wash zone contactingstructure by means of a collection apparatus disposed below the washzone and above the feed zone; withdrawing the slop wax from thecollection apparatus to a slop wax pump; conducting at least a portionof a slop wax pump discharge liquid to the wash oil distributor at arate sufficient to assure thorough wetting of the wash oil liquid/vaporcontacting structure and to substantially eliminate entrained liquid orsolid particles from vapor rising from the wash zone; and adding to theslop wax stream conducted to the wash oil distributor only enough of aheaviest distillate product as makeup to maintain a liquid level on theslop wax collection apparatus.
 2. The process of claim 1, wherein thewash zone irrigated only by the slop wax and the makeup distillate, ifany, comprises the sole means of removing entrained liquid or solidsfrom the vapor rising from the feed zone, thereby minimizing the amountof distillate product downgraded by use as wash oil, and the vaporrising from the wash zone is substantially free of entrainednon-volatile material.
 3. The process of claim 1, wherein enough heat isremoved from the wash oil stream to condense in the wash zone enough ofthe feed vapor to maintain the level on the slop wax collectionapparatus without using any distillate as makeup to the wash zone. 4.The process of claim 1, wherein a liquid collection apparatus isprovided above the wash zone to collect downflowing liquid and aninsulating material is applied to the liquid collection apparatus abovethe wash zone to reduce condensation on the lower surface of thecollection apparatus of feed vapor rising from the wash zone, therebyincreasing the fraction of feed vapor that passes through the collectionapparatus to be condensed and yielded as distillate product.
 5. Theprocess of claim 4, wherein the insulating material is applied to anupper surface of a floor of the liquid collection apparatus.
 6. Aprocess for improving quality and yield of one or more distillateproducts drawn from a distillation column whose feed stream is a mixtureof vapor and a liquid containing one or more components that aresubstantially non-volatile at column conditions, the distillation columncomprising a feed zone, a wash zone located above the feed zone havingdisposed therein a liquid/vapor contacting structure and above it a washoil distributor for distributing wash oil to the upper surface of thecontacting structure, and means above the wash zone to remove vaporproduct or liquid condensed therefrom, the process comprising:collecting liquid slop wax falling from the wash zone contactingstructure by means of a collection apparatus disposed below the washzone and above the feed zone; withdrawing the collected slop wax fromthe collection apparatus to a slop wax pump; conducting at least aportion of the withdrawn slop wax to the wash oil distributor at a ratesufficient to assure thorough wetting of the wash oil zone liquid/vaporcontacting structure and to substantially eliminate entrained liquid orsolid particles from the vapor rising from the wash zone; and removingenough heat from the recirculated slop wax to condense in the wash zoneenough of the feed vapor to maintain a liquid level on the slop waxcollection apparatus.
 7. The process of claim 6, wherein the vaporproduct rising from the wash zone is substantially free of entrainednon-volatile material and the wash zone irrigated by wash oil comprisingonly recirculated slop wax plus the liquid condensed in the wash zonefrom the feed vapor comprises the sole means of removing entrainedliquid or solids from the vapor rising from the feed zone.
 8. Theprocess of claim 6, wherein a liquid collection apparatus is providedabove the wash zone to collect downflowing liquid and an insulatingmaterial is applied to the collection apparatus to reduce condensationon the lower surface of the collection apparatus of the vapor productrising from the wash zone, thereby increasing the fraction of feed vaporthat passes through said collection apparatus to be yielded asdistillate product essentially free of entrained contaminants.
 9. Theprocess of claim 8, wherein the insulating material is applied to anupper surface of a floor of the collection apparatus.
 10. A process forreducing the amount of clean wash liquid required to effectivelyeliminate from a vapor stream entrained liquid or solid material and theamount of contaminated wash liquid produced from a columnar liquid/vaporcontacting device whose feed stream is a mixture of vapor and a liquidor solid containing one or more components that are substantiallynon-volatile at column conditions and which would be deleterious to thevapor product or liquid condensed therefrom, where at least one of theobjectives of the column is to remove the entrained phase from the vaporrising from the feed zone, the column comprising a feed zone, a washzone located above the feed zone having disposed therein a liquid/vaporcontacting structure and above it a wash liquid distributor fordistributing wash liquid to the upper surface of the contactingstructure, and above the wash liquid distributor, a means for removingthe vapor or liquid condensed from same, the process comprising:collecting liquid falling from the wash zone contacting structure,containing material previously entrained in the rising vapor, by meansof a liquid collection apparatus disposed below the wash zone and abovethe feed zone; withdrawing the wash zone liquid from said collectionapparatus to a wash liquid pump; conducting at least a portion of thewash liquid pump discharge liquid to the wash liquid distributor at arate sufficient to substantially eliminate entrained liquid or solidparticles from the vapor rising from the wash zone, whereinsubstantially all entrained non-volatile material is effectivelyeliminated from the rising vapor and concentrated in the wash zonewithdrawn liquid, and wherein the wash zone irrigated by wash liquidcomprising recirculated wash zone outlet liquid comprises the sole meansof removing entrained liquid or solids from the vapor rising from thefeed zone.
 11. The process of claim 10, wherein a portion of thewithdrawn wash zone liquid is removed from the columnar liquid/vaporcontacting device to carry the captured entrained material to anexternal destination.
 12. The process of claim 10, wherein at least aportion of the recirculated wash zone outlet liquid is filtered toremove solids and the filtrate is passed to the wash liquid distributor.